Marcelo O. Rodrigues

Cytotoxicity and slow release of the anti-cancer drug doxorubicin from ZIF-8

Metal–organic frameworks are emerging as a powerful platform for the delivery and controlled release of several drug molecules. Herein, we report the incorporation of the anti-cancer drug doxorubicin into the zeolitic imidazolate framework (ZIF-8) with high-load and progressive release. Adsorption measurements show that doxorubicin is incorporated into ZIF-8 with a load of 0.049 g doxorubicin g−1 dehydrated ZIF-8. Doxorubicin is released in a highly controlled and progressive fashion with 66% of the drug released after 30 days. We also characterize the antitumoral potential and cytotoxicity of the doxorubicin-ZIF-8 (DOXO-ZIF-8) complex towards the mucoepidermoid carcinoma of human lung (NCI-H292), human colorectal adenocarcinoma (HT-29), and human promyelocytic leukemia (HL-60) cell lines. It is shown that the complex doxorubicin-ZIF-8 exhibits lower cytotoxicity than pure doxorubicin for the tested cells, possibly due to the slower release of the incorporated drug. Furthermore, host–guest interactions have been addressed from a microscopic perspective through molecular docking simulations. In conjunction with our experimental characterization, the calculations suggest that doxorubicin binds preferentially to the surface rather than into the pores of ZIF-8, whose entry diameter is at least half the size of the shortest axis of the drug. These findings are also consistent with high-resolution X-ray crystallography and NMR spectroscopy studies of ZIF-8 which shows that this framework is very rigid under constant pressure in contrast to previous experimental and theoretical studies of ZIF-8 under gas pressure.

Theoretical and Experimental Studies of the Photoluminescent Properties of the Coordination Polymer [Eu(DPA)(HDPA)(H2O)2]·4H2O

We report on the hydrothermal synthesis of the [Eu(DPA)(HDPA)(H(2)O)(2)].4H(2)O lanthanide-organic framework (where H2DPA stands for pyridine-2,6-dicarboxylic acid), its full structural characterization including single-crystal X-ray diffraction and vibrational spectroscopy studies, plus detailed investigations on the experimental and predicted (using the Sparkle/PM3 model) photophysical luminescent properties. We demonstrate that the Sparkle/PM3 model arises as a valid and efficient alternative to the simulation and prediction of the photoluminescent properties of lanthanide-organic frameworks when compared with methods traditionally used. Crystallographic investigations showed that the material is composed of neutral one-dimensional coordination polymers infinity(1)[Eu(DPA)(HDPA)(H(2)O)(2)] which are interconnected via a series of hydrogen bonding interactions involving the water molecules (both coordinated and located in the interstitial spaces of the structure). In particular, connections between bilayer arrangements of infinity(1)[Eu(DPA)(HDPA)(H(2)O)(2)] are assured by a centrosymmetric hexameric water cluster. The presence of this large number of O-H oscillators intensifies the vibronic coupling with water molecules and, as a consequence, increases the number of nonradiative decay pathways controlling the relaxation process, ultimately considerably reducing the quantum efficiency (eta = 12.7%). The intensity parameters (Omega(2), Omega(4), and Omega(6)) were first calculated by using both the X-ray and the Sparkle/PM3 structures and were then used to calculate the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield obtained from the X-ray and Sparkle/PM3 structures (both of about 12.5%) are in good agreement with the experimental value (12.0 +/- 5%). These results clearly attest for the efficacy of the theoretical models employed in all calculations and create open new interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Modeling, Structural, and Spectroscopic Studies of Lanthanide-Organic Frameworks

In this paper, we report the hydrothermal synthesis of three lanthanide-organic framework materials using as primary building blocks the metallic centers Eu(3+), Tb(3+), and Gd(3+) and residues of mellitic acid: [Ln(2)(MELL)(H(2)O)(6)] (where Ln(3+) = Eu(3+), Tb(3+), and Gd(3); hereafter designated as (1), (2) and (3)). Structural characterization encompasses single-crystal X-ray diffraction studies, thermal analysis, and vibrational spectroscopy, plus detailed investigations on the experimental and predicted (using the Sparkle/AM1 model) photophysical luminescent properties. Crystallographic investigations showed that the compounds are all isostructural, crystallizing in the orthorhombic space group Pnnm and structurally identical to the lanthanum 3D material reported by the group of Williams. (2) is highly photoluminescent, as confirmed by the measured quantum yield and lifetime (37% and 0.74 ms, respectively). The intensity parameters (Omega(2), Omega(4), and Omega(6)) of (1) were first calculated using the Sparkle/AM1 structures and then employed in the calculation of the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield derived from the Sparkle/AM1 structures was approximately 16%, and the experimental value was 8%. We attribute the registered differences to the fact that the theoretical model does not consider the vibronic coupling with O-H oscillators from coordinated water molecules. These results clearly attest for the efficacy of the theoretical models employed in all calculations and open a new window of interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

High photoluminescent metal-organic frameworks as optical markers for the identification of gunshot residues.

Gunshot residue (GSR) are solid particles produced when a firearm is discharged, and its detection is important evidence in forensic investigations. Currently, scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS) is the standard technique adopted for the analysis and identification of GSR; however, this methodology is inefficient for lead-free ammunition. Herein, we report the inclusion of high photoluminescent metal-organic frameworks in ammunition to allow for the visual detection of GSR. The tests indicated that marked GSR is easily visible in proportions above 5.0 wt %. A total of 1 g of marker suffices to tag 100 0.38 mm bullets or 62 0.40 mm bullets.

Potential of a metal-organic framework as a new material for solid-phase extraction of pesticides from lettuce (Lactuca sativa), with analysis by gas chromatography-mass spectrometry.

The metal-organic framework (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] was tested for extraction of pyrimicarb, procymidone, malathion, methyl parathion and α- and β-endosulfan from lettuce, with analysis using GC/MS in SIM mode. Experiments were carried out in triplicate at two fortification levels (0.1 and 0.5 mg/kg), and resulted in recoveries in the range of 78-107%, with RSD values between 1.6 and 8.0% for (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] sorbent. Detection and quantification limits ranged from 0.02 to 0.05 mg/kg and from 0.05 to 0.10 mg/kg, respectively, for the different pesticides studied. The method developed was linear over the range tested (0.05-10.0 μg/mL), with correlation coefficients ranging from 0.9990 to 0.9997. Comparison between (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] and conventional sorbent (silica gel) showed better performance of the (∞)[(La(0.9)Eu(0.1))(2)(DPA)(3)(H(2)O)(3)] polymeric sorbent for all pesticides tested.

Theoretical and Experimental Spectroscopic Approach of Fluorinated Ln3+−β-Diketonate Complexes

In this paper we report the synthesis of two new complexes, [Eu(fod)(3)(phen)] and [Tb(fod)(3)(phen)] (fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadionate and phen = 1,10-phenanthroline), and their complete characterization, including single-crystal X-ray diffraction, UV-vis spectroscopy, IR spectroscopy, and TGA. The complexes were studied in detail via both theoretical and experimental approaches to the photophysical properties. The [Eu(fod)(3)(phen)] complex crystallizes in the monoclinic space group P2(1)/c. The crystal structure of [Eu(fod)(3)(phen)] exhibits an offset pi-pi stacking interaction between the phenanthroline ligands of adjacent lanthanide complexes. The Eu(3+) cation is coordinated to three fod anionic ligands and to one phen. The symmetry around Eu(3+) is best described as a highly distorted square antiprism. The molar absorption coefficients of [Eu(fod)(3)(phen)] and [Tb(fod)(3)(phen)] revealed an improved ability to absorb light in comparison with the stand-alone phen and fod molecules. [Tb(fod)(3)(phen)] emits weak UV excitation, with this feature being explained by the triplet-(5)D(4) resonance, which contributes significantly to the nonradiative deactivation of Tb(3+), causing a short lifetime and low quantum yield. The intensity parameters (Omega(2), Omega(4), and Omega(6)) of [Eu(fod)(3)(phen)] were calculated for the X-ray and Sparkle/AM1 structures and compared with values obtained for [Eu(fod)(3)(H(2)O)(2)] and [Eu(fod)(3)(phen-N-O)] (phen-N-O = 1,10-phenanthroline N-oxide) samples. Intensity parameters were used to predict the radiative decay rate. The theoretical quantum efficiencies from the X-ray and Sparkle/AM1 structures are in good agreement with the experimental values, clearly attesting to the efficacy of the theoretical models.

Two-dimensional coordination polymer matrix for solid-phase extraction of pesticide residues from plant Cordia salicifolia

The 2D coordination polymer (infinity[Gd(DPA)(HDPA)]) was tested for extraction of acephate, chlorpropham, pirimicarb, bifenthrin, tetradifon, and phosalone from the medicinal plant Cordia salicifolia, whose extracts are commercialized in Brazil as diuretic, appetite suppressant, and weight loss products, using GC/MS, SIM. Considering that there are no Brazilian regulations concerning maximum permissible pesticide residue concentrations in medicinal herbs, recovery experiments were carried out (seven replicates), at two arbitrary fortification levels (0.5 and 1.0 mg/kg), resulting in recoveries in range of 20 to 107.7% and SDRSDs were between 5.6 and 29.1% for infinity[Gd(DPA)(HDPA)] sorbent. Detection and quantification limits for herb ranged from 0.10 to 0.15 mg/kg and from 0.15 to 0.25 mg/kg, respectively, for the different pesticides studied. The developed method is linear over the range assayed, 0.5-10.0 microg/mL, with correlation coefficients ranging from 0.9975 to 0.9986 for all pesticides. Comparison between infinity[Gd(DPA)(HDPA)] sorbent and conventional sorbent (neutral alumina) showed similar performance of infinity[Gd(DPA)(HDPA)] polymeric sorbent for three (bifenthrin, tetradifon, and phosalone) out of six pesticides tested.

Up-conversion properties of lanthanide-organic frameworks and how to track ammunitions using these materials

This manuscript reports the first example of up-conversion properties involving Yb3+ and Tb3+ ions in five isostructural Lanthanide-Organic Frameworks (LnOFs), herein designated as UCMarker-1 to UCMarker-5, respectively, and their application as optical probes for the identification of gunshot residues (GSRs) and the ammunition encryption procedure. The excitation of the Yb3+ 2F7/2 ↔ 2F5/2 transition (980 nm) at room temperature leads to visible up-conversion (UC) emission of Tb3+ 5D4 → 7FJ. The GSR and lead-free primer residues are easily identified upon UV radiation (λ = 254 nm). These results prove that the exploration of LnOFs to identify GSR is attractive for the identification of ammunition origins or caliber recognition.

Inkjet Printing of Lanthanide–Organic Frameworks for Anti-Counterfeiting Applications

Photoluminescent lanthanide-organic frameworks (Ln-MOFs) were printed onto plastic and paper foils with a conventional inkjet printer. Ln-MOF inks were used to reproduce color images that can only be observed under UV light irradiation. This approach opens a new window for exploring Ln-MOF materials in technological applications, such as optical devices (e.g., lab-on-a-chip), as proof of authenticity for official documents.

Multifunctional micro- and nanosized metal–organic frameworks assembled from bisphosphonates and lanthanides

Phase-pure and highly crystalline [Ln(Hpmd)(H2O)] materials [where Ln3+ = Eu3+ (1), Gd3+ (2) and Tb3+ (3); H4pmd = 1,4-phenylenebis(methylene)diphosphonic acid] were prepared by using three distinct approaches: (i) conventional hydrothermal synthesis (180 °C, 3 days); (ii) microwave-assisted heating (50 W irradiation power, 40 °C, 5 seconds; nano-sized aggregates with sizes ranging between 100 and 150 nm); and (iii) ultrasound-assisted synthesis which, for highly diluted reactive mixtures (Ln3+ : H4pmd : H2O of 1 : 1 : 7200), permitted the preparation of isolated nano-crystals at ambient temperature with 5 minutes of ultrasonic irradiation. Compounds were structurally characterized by powder X-ray diffraction (Rietveld refinement and variable-temperature studies), thermogravimetry, vibrational spectroscopy, elemental analysis and electron microscopy (SEM and EDS). The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K revealing that the Ln3+ cations act as isolated centers. A strategy to calculate the vibrational spectra of MOF structures and based on the known embedded-clusters approach is proposed and applied to [Ln(Hpmd)(H2O)]. This allowed the identification, along with deuteration of the materials, of the vibrational modes of the confined water molecule in the structure. Compound 1 was tested in the methanolysis of styrene oxide at 55 °C: it is shown that microcrystalline 1 (1-m) does not possess significant catalytic activity; on the other hand, the nano-sized counterpart (1-n) exhibits relatively high catalytic activity and excellent selectivity to 2-methoxy-2-phenylethanol (100% yield within 48 h of reaction time). Photoluminescence studies both at ambient and low temperatures showed, on the one hand, that bulk materials are composed of a single lanthanide site and, on the other hand, that the organic linker is a suitable sensitizer of Tb3+ (absolute quantum yield of ca. 14% for 3). It is further demonstrated that the coordinated water molecule has a pivotal role in the quenching of the photoluminescence of Eu3+ in 1: deuteration of the material results in a ca. 3.4 times improvement of the decay time (e.g., at 300 K the lifetime improves from 0.58 ± 0.01 ms to 1.98 ± 0.01 ms).